Orientation as a probe of photodissociation dynamics

Molecular chlorine (Cl-2) was photodissociated in the wavelength range 270- 400 nm with linearly polarized light, and the orientation of the excited-st ate chlorine atom Cl*(P-2(1/2)) was measured by 2+1 resonance enhanced mult iphoton ionization (REMPI) using circularly polarized light. The degree of orientation of the Cl* photofragment is found to oscillate as a function of photolysis wavelength. The oscillation is a result of quantum mechanical c oherence arising from electronic states of different symmetry that correlat e to the same separated-atom asymptote. A simple curve-crossing model using ab initio potential energy curves reproduces the general shape of the osci llation but fails to give a quantitative fit.